The aminoglycoside antibiotics are extremely useful in the treatment of gram-negative sepsis, and their clinical utility is associated with dose- limiting nephrotoxicity. The studies to be performed will employ a cell culture model of the human proximal tubule to determine the cellular basis of aminoglycoside-induced nephrotoxicity. The studies proposed will test the hypothesis that the nephrotoxicity of the aminoglycoside antibiotics results from a failure of the proximal tubule cell to maintain ion homeostasis. Central to this hypothesis is an aminoglycoside-induced alteration in proximal tubule sodium-dependent transport processes. It is well known that the degree on the polarization and differentiation of the epithelial cell. It is proposed that highly-differentiated proximal tubule cells are dependent of these sodium-dependent processes and susceptible to aminoglycoside-induced alteration in these processes. However, upon aminoglycoside-induced necrosis, these highly-differentiated cells are replaced by more primitive epithelial cells that are not yet polarized. It is postulated that these cells are not reliant on sodium-dependent processes and, thus, are resistant to the aminoglycosides. Preliminary data is presented to support this hypothesis. Of central significance is the fact that this hypothesis would explain the well-known observation that aminoglycoside-induced nephrotoxicity and cell regeneration occur as a simultaneous event in the clinical and animal model settings. This hypothesis would be supported by completion of specific aims designed to demonstrate: 1. a general alteration in sodium-dependent transport processes as a function of aminoglycoside exposure, 2. an increased aminoglycoside toxicity when cells are exposed to agents which increase sodium-dependent transport processes, and 3. aminoglycoside-induced alterations in the electrical and structural properties of the cell membrane that are consistent with an alteration in sodium-dependent transport processes.